Fix unqualified column references.

Fix various places to avoid unqualified column references to prevent any
potential ambiguous column errors.

app/models/news_update.rb

@@ -3,7 +3,7 @@
 class NewsUpdate < ApplicationRecord
   belongs_to :creator, class_name: "User"
   belongs_to_updater
-  scope :recent, -> {where("created_at >= ?", 2.weeks.ago).order("created_at desc").limit(5)}
+  scope :recent, -> {where("created_at >= ?", 2.weeks.ago).order(created_at: :desc).limit(5)}
 
   def self.visible(user)
     if user.is_admin?